This invention relates to a multi-piece solid golf ball offering satisfactory distance, feel on impact and controllability, and having improved crack durability against repeated shots and improved scuff resistance.
Golf balls of various structures are known in the art. In particular, a number of proposals have been made on solid golf balls, inter alia, multi-piece solid golf balls having a core enclosed with a plurality of layers on account of flight distance, controllability (or spin rate) and feel.
JP-A 7-24085 proposes a golf ball having an outer layer and an intermediate layer which are both made of low specific gravity ionomer cover stocks, but leaving problems with respect to impact durability against repeated shots and scuff resistance.
JP-A 11-104273 proposes a golf ball having an outer layer which is a high specific gravity urethane cover and an intermediate layer which is an ionomer layer. Since the hardnesses of the respective layers are insufficiently optimized and the materials used are insufficient to satisfy the desired performance, there are left problems in satisfying all the factors of flight, feel, controllability, impact durability and scuff resistance.
An object of the present invention is to provide a multi-piece solid golf ball which satisfies all the factors of flight, feel and controllability required by ordinary amateur users who intend to play in competition, and offers both shot durability against repeated shots and scuff resistance at a high level.
Making extensive investigations to attain the above object, the inventor has discovered with respect to a multi-piece solid golf ball comprising a core, an intermediate layer enclosing the core, and an outer layer or cover enclosing the intermediate layer, that a golf ball satisfying all the factors of flight, feel, controllability, crack durability and scuff resistance is obtained by using a thermoplastic resin composition in the intermediate layer, and optimizing the Shore D hardness of intermediate layer surface, intermediate layer""s specific gravity, outer layer""s specific gravity, core""s specific gravity, the total gauge of intermediate layer and outer layer, a hardness difference between core surface JIS-C hardness and core center JIS-C hardness, a hardness difference between intermediate layer surface JIS-C hardness and core surface JIS-C hardness, and a hardness difference between outer layer surface Shore D hardness and intermediate layer surface Shore D hardness. The present invention is predicated on this discovery.
Accordingly, the invention provides a golf ball as defined below.
[I] A multi-piece solid golf ball comprising a core, an intermediate layer enclosing the core, and an outer layer enclosing the intermediate layer, characterized in that the intermediate layer is made of a thermoplastic resin composition, the intermediate layer on its surface has a Shore D hardness of at least 57, the intermediate layer has a specific gravity of 1.00 to 1.30 g/cm3, the outer layer has a specific gravity of at least 1.00 g/cm3, the core has a specific gravity of 1.05 to 1.20 g/cm3, the intermediate layer and the outer layer have a total gauge of up to 3.3 mm, the core at its surface and center, the intermediate layer at its surface, and the outer layer at its surface have hardnesses satisfying: [(core surface JIS-C hardness)xe2x88x92(core center JIS-C hardness)]xe2x89xa716, [(intermediate layer surface JIS-C hardness)xe2x88x92(core surface JIS-C hardness)]20, and xe2x88x9218xe2x89xa6[(outer layer surface Shore D hardness)xe2x88x92(intermediate layer surface Shore D hardness)] less than 0.
[II] The multi-piece solid golf ball of [I] wherein the core center has a JIS-C hardness of 54 to 66, and the core surface has a JIS-C hardness of 72 to 95.
[III] The multi-piece solid golf ball of [I] or {II] wherein the outer layer is made of a polyurethane composition.
[IV] The multi-piece solid golf ball of [I], [II] or [III] wherein said thermoplastic resin composition comprises a thermoplastic resin and an inorganic particulate filler in a proportion of 100/5 to 100/25 by weight ratio.
[V] The multi-piece solid golf ball of [IV] wherein said thermoplastic resin composition comprises (A) an ionomer resin component which contains (a-1) an olefin/unsaturated carboxylic acid random bipolymer and/or a metal ion neutralization product of an olefin/unsaturated carboxylic acid random bipolymer and (a-2) an olefin/unsaturated carboxylic acid/unsaturated carboxylic acid ester random terpolymer and/or a metal ion neutralization product of an olefin/unsaturated carboxylic acid/unsaturated carboxylic acid ester random terpolymer, and (B) a non-ionomer thermoplastic elastomer.
[VI] The multi-piece solid golf ball of [IV] or [V] wherein said thermoplastic resin composition comprises (A) the ionomer resin component which contains components (a-1) and (a-2) in a proportion (a-1)/(a-2) of 100/0 to 25/75 by weight ratio, and (B) the non-ionomer thermoplastic elastomer in a proportion (A)/(B) of 100/0 to 50/50 by weight ratio.
[VII] The multi-piece solid golf ball of any one of [III] to [VI] wherein said polyurethane composition contains (C) a thermoplastic polyurethane and (D) an isocyanate mixture, said isocyanate mixture (D) is a mixture prepared by dispersing (d-1) a compound having as functional groups at least two isocyanate groups per molecule in (d-2) a hermoplastic resin that is substantially non-reactive with isocyanate.
[VIII] The multi-piece solid golf ball of any one of [I] to [VIII] wherein said core has a two-layer structure.
[IX] The multi-piece solid golf ball of any one of [I] to [VIII] wherein [(core surface JIS-C hardness)xe2x88x92(core center JIS-C hardness)]xe2x89xa720.